zlacker

You already can't run modems over the phone network anymore. Modern noise reduction algorithms helpfully remove as much modem data as they can.

>>kuschk+(OP)
Now I kind of want to build one just for the challenge. Analyze what frequencies can get through, and reverse engineer the phone company's codec so I can send a pirate signal, like a phreaker of old.

Fun fact: You can no longer do such a project in software on stock Android. They locked down the voice audio API.